The present invention relates to the methods and systems for the automatic control of the cutting off and restarting of the thermal engine of a vehicle during temporary immobilisations of the latter.
Such an automatic control, conventionally referred to as xe2x80x9cstop and goxe2x80x9d according to the English terminology used by persons skilled in the art, consists of stopping the thermal engine during temporary immobilisations of the vehicle, such as for example at a red light or a level crossing, or in traffic bottlenecks.
One possible control consists of automatically stopping the thermal engine when the vehicle has been at rest for a certain amount of time, whilst the gearbox is in neutral and the accelerator and clutch are in the idle position, and then automatically restarting the thermal engine when the driver presses on the accelerator or brake pedal, or changes to a gear ratio other than neutral.
During these more or less long periods during which the thermal engine is temporarily stopped, the alternator does not rotate and the battery discharges to a greater or lesser extent according to the current consumption in the various vehicle circuits.
Because of this, in the case of difficult road traffic, or in the case of high electrical consumption, the battery may reach a discharge level such that restarting is no longer possible.
The vehicle is then broken down.
To limit this risk, the known solutions consist of using batteries of higher capacity in order to increase the reserve of electrical energy or to use a higher-power alternator in order to recharge the battery more rapidly during the periods of operation of the engine.
The result is an enhancement of the electrical equipment and significant extra costs.
To this end, a method has been proposed, in the document WO 98/14702, for controlling the thermal engine of a motor vehicle according to which the thermal engine is cut off and automatically restarted at the beginning and end of periods of temporary immobilization, and according to which the automatic cutting off of the thermal engine is inhibited when the vehicle battery is discharged below a given inhibition threshold.
It may be desirable to reduce the power of the battery and alternator even further.
The object of the present invention is to meet this requirement simply and economically.
According to the invention a method of the type indicated above is characterised in that the thermal engine is restarted automatically when the battery is discharged below the inhibition threshold.
Thus recharging of the battery occurs even when the vehicle is waiting at a light.
This arrangement makes it possible not to oversize the battery and therefore the alternator which recharges the battery.
Thus, in the case where the engine is stopped, the gearbox being in neutral and the clutch pedal idle, whilst the ignition key is in the operating position, an instruction to restart the engine is issued in order to recharge the battery if a measurement of the battery voltage indicates a voltage below a threshold.
In the case where the engine is running, the instruction to stop the engine is ignored when the battery voltage measured is below the said threshold.
The risks of breakdown are therefore prevented.
The invention is advantageously supplemented by the following different characteristics, taken alone or according to all possible technical combinations thereof:
inhibition of the automatic cutting off of the thermal engine is cancelled when the battery charge level is above a given threshold greater than or equal to the inhibition threshold;
the battery charge level is characterised by the voltage thereof measured periodically, when the thermal engine is not operating;
the battery charge level is characterised by the drop in voltage of the battery when the starter is activated and before the electric motor thereof is actuated;
the battery charge level is characterised by the voltage drop in the battery when the electric motor of the starter is rotated;
the battery charge level is characterised by the average voltage drop during the driving of the thermal engine by the electric motor of the starter;
the battery charge level is characterised by the speed of driving of the starter.
The invention also proposes a system for controlling the thermal engine of a motor vehicle having means for detecting the start and end of temporary immobilisation periods and for cutting off and automatically restarting the said thermal engine when the start or end of such a period is detected, characterised in that it has means for implementing such a method.
Other characteristics and advantages of the invention will also emerge from the following description. This description is purely illustrative and non-limitative. It must be read with regard to the accompanying single figure which depicts a flow diagram of a command in accordance with one possible embodiment of the invention.